An order to buy or sell a security (stock, bond, etc.) in a non-standard amount- i.e., not a multiple of the standard amount per order (standard order unit). For example, the standard order unit for stocks is 100 shares or its multiples for an order. Therefore, an order to buy or sell 125 shares is an odd lot (in which 100 constitutes a standard lot or the so-called round lot and 25 remain to be filled as a non-standard lot). Likewise, an order on 450 shares consists of 4 round lots (4 ×100 or 400 shares) and 1 odd lot (50 shares).

For bonds, the standard lot is five bonds.

Odd lot is also known as uneven lot or broken lot.